A sensitive method for measuring de- and remineralization of tooth enamel under intraoral conditions will be used to assess the protective effect of saliva against acid dissolution. The intraoral effect of fluoride on enamel-saliva interaction will also be studied. In addition, the method which involves determination of the permeability of enamel to iodide, will be employed to measure the cariogenic potential of foods under intraoral conditions. For this purpose, blocks of bovine enamel will be carried on a prosthesis which permits normal mastication and salivation. The blocks are covered by a thin layer of a pure culture of S. mutans or organisms recovered from the subject's saliva. The acid generated by the organisms upon exposure to fermentable carbohydrate causes demineralization of the enamel, readily detected as an increase in permeability to iodide. Tests of liquid and solid foods can usually be performed in 1 to 3 hr. The cariogenicity of different concentrations of the most commonly used sugars, will be determined. Raw and gelatinized starches will also be investigated. Factors believed to influence the cariogenicity of foods, including physical attributes, such as those influencing their oral retention, food proteins and lipids, buffering capacity and acidity and effects on saliva will be studied by testing a lean formula cookie, and adding various ingredients to the cookie, one at a time to change its composition and consistency. In addition, the study will be concerned with the effect on cariogenicity of increased salivary flow, the use of mouthrinses or foods which may modify the cariogenic challenge. The cariostatic mechanism of fluoride and various phosphate compounds will also be investigated.